This invention relates to a friction modifier for use in fuels, particularly in gasolines for internal combustion engines. The present invention further relates to new spark-ignition fuel compositions including such a friction modifier and methods for controlling, i.e., reducing or eliminating, deposits and wear in engines, fuel pumps and injectors while imparting enhanced fuel economy performance.
Over the years considerable work has been devoted to additives for controlling (preventing or reducing) deposit formation in the fuel induction systems of spark-ignition internal combustion engines. In particular, additives that can effectively control fuel injector deposits, intake valve deposits and combustion chamber deposits represent the focal point of considerable research activities in the field and despite these efforts, further improvements are desired.
Conventional port-fuel injection (PFI) engines form a homogeneous pre-mixture of gasoline and air by injecting gasoline into the intake port, while direct injection gasoline (DIG) engines inject gasoline directly into the combustion chamber like a diesel engine so that it becomes possible to form a stratified fuel mixture which contains greater than the stoichiometric amount of fuel in the neighborhood of the spark plug but highly lean in the entire combustion chamber. Due to the formation of such a stratified fuel mixture, combustion with the overall highly lean mixture can be achieved, leading to an improvement in fuel consumption over that of PFI engines, and approaching that of diesel engines.
The major fuel-related deposit problem areas for PFI and DIG engines are injectors, intake valves, and the combustion chamber. Additionally, engine friction between piston and cylinder, the valve train, and the fuel pump result in increasing fuel consumption. In DIG engine technology in particular there is a friction related durability issue with the high-pressure pump (up to 1500 psi pumping capacity), which break down due to the inherently low lubricity of gasolines. There is, therefore, a desire in the petroleum industry to produce a fuel suitable for use in both PFI and DIG engines, that can address the engine deposit and frictional requirements outlined above.
As discussed at some length in U.S. Pat. No. 6,277,158 to McLean, the performance of gasolines and other fuels can be improved through the use of additive technology. For instance, detergents have been used to inhibit the formation of intake system deposits, and thereby improve engine cleanliness and performance. Regulatory mandates have required the introduction of low sulfur fuels, which are known to be less lubricating and raise concerns regarding the durability of fuel pumps and injectors. Sulfur itself is not directly known to be a lubricity modifying agent. However, removal of sulfur by deep hydrotreating is known to also inadvertently remove natural lubricity components of the fuel, such as certain aromatics, carboxylic acids, and esters. Unfortunately, commercial gasoline detergents and dispersants generally show very little friction reducing characteristics until very high concentrations of them are added to the fuel. These high detergent concentrations often reach levels where no-harm effects such as CCD become unacceptable.
It has been suggested that separate friction modifiers can be added to gasoline to increase fuel economy by reducing engine friction. Fuel friction modifiers would also serve to protect high-pressure fuel pumps and injectors such as those found in DIG engines from wear caused by fuel. Worldwide regulations calling for a steep reduction in fuel sulfur levels may exacerbate this wear problem even further. In selecting suitable components for a combined detergent/friction modifier additive package it is important to ensure a balance of detergent and friction modification properties, and so forth. Ideally, the friction modifier should not adversely affect the deposit control function of the detergent. In addition the additive package should not adversely effect on engine performance. For example, the additive package should not promote valve sticking or cause other performance-reducing problems. To be suitable for commercial use, the friction modifier additive also must pass all no-harm testing required for gasoline performance additives. This is often the biggest hurdle for commercial acceptance. The no-harm testing involves 1) compatibility with gasoline and other additives likely to be in gasoline at a range of temperatures, 2) no increase in IVD and CCD, 3) no valve stick at low temperatures, and 4) no corrosion in the fuel system, cylinders, and crankcase. Developing an additive meeting all these criteria is challenging.
Most prior friction modifiers for fuels have been derivatives of natural product (plant and animal derived) fatty acids, with only a few purely synthetic products. For example, WO 01/72930 A2 describes a mechanistic proposal for delivery of a fuel born friction modifier to the upper cylinder wall and into the oil sump resulting in upper cylinder/rings and valves lubrication. The friction modifier is packaged with fuel detergent dispersants such as polyetheramines (PEAs), polyisobutene amines (PIBAs), Mannich bases, and succinimides. Fuel friction modifier prior art identified in the WO '930 reference include U.S. Pat. Nos. 2,252,889, 4,185,594, 4,208,190, 4,204,481, and 4,428,182, which all describe use of fuel modifiers in diesel fuel. Chemistries covered by these patents include fatty acid esters, unsaturated dimerized fatty acids, primary aliphatic amines, fatty acid amides of diethanolamine and long-chain aliphatic monocarboxylic acids. Another specific mentioned patent therein is U.S. Pat. No. 4,427,562, which discloses a lubricant oil and fuel friction modifier made by reacting primary alkoxyalkylamines with carboxylic acids or by aminolysis of the appropriate formate ester, and also U.S. Pat. No. 4,729,769.
U.S. Pat. No. 4,729,769, describes a gasoline carburetor detergent for gasoline compositions derived from reaction products of a C6-C20 fatty acid ester, such as coconut oil, and a mono- or di-hydroxy hydrocarbyl amine, such as diethanolamine, as carburetor detergents. The additive in the '769 patent is described as being useful in any gasoline including leaded and those containing methylcyclopentadienyl manganese tricarbonyl (MMT). The fuel described in the '769 patent may contain other necessary additives such as anti-icers, and corrosion inhibitors.
U.S. Pat. No. 5,858,029 describes friction reducing additives for fuels and lubricants involving the reaction products of primary etheramines with hydrocarboxylic acids to give hydroxyamides that exhibit friction reduction in fuels and lubricants. Other prior patents describing friction modifiers include U.S. Pat. No. 4,617,026 (monocarboxylic acid of ester of a trihydric alcohol, glycerol monooleate as fuels and lubricant friction modifier); U.S. Pat. Nos. 4,789,493, 4,808,196, and 4,867,752 (use of fatty acid formamides); U.S. Pat. No. 4,280,916 (use of fatty acid amides); U.S. Pat No. 4,406,803 (use of alkane 1,2-diols in lubricants to improve fuel economy); and U.S. Pat. No. 4,512,903 (use of amides from mono- or polyhydroxy substituted aliphatic monocarboxylic acids and amines). U.S. Pat. No. 6,328,771 discloses fuel compositions containing lubricity enhancing salt compositions made by the reaction of certain carboxylic acids with a component that is comprised of a heterocyclic aromatic amine. EP 0 798 364 discloses diesel fuel additives comprising a salt of a carboxylic acid and an aliphatic amine, or an amide obtained by dehydration-condensation between a carboxylic acid and an aliphatic amine.
EP 0 869 163 A1 describes a method for reducing engine friction by use of ethoxylated amines. In addition, U.S. Pat. No. 4,086,172 (oil soluble hydroxyamines such as “ETHOMEEN 18-12™” formula C18H37N—(CH2CH2OH)2 as lubricant antioxidant); U.S. Pat. No. 4,129,508 (reaction products of succinic acid or anhydride and a polyalkylene glycol or monoether, an organic basic metal, and an alkoxylated amine as a demulsifier); U.S. Pat. Nos. 4,231,883; 4,409,000; and 4,836,829, all teach various uses of hydroxyamines in fuels and lubricants.
U.S. Pat. No. 6,277,158 describes the current practice in the supply of gasoline as generally being to pre-mix the fuel additives into a concentrate in a hydrocarbon solvent base, and then to inject the concentrate into gasoline pipelines used to fill tankers prior to delivery to the customer. To facilitate injection of the concentrate into the gasoline, it is important that the concentrate is in the form of a low viscosity, homogeneous liquid.
A friction modifier may be added to the gasoline as the lone additive or in combination with a detergent dispersant package that is fully formulated for fuel compatibility at conditions likely to be experienced by the engine. In addition, a need may exist for a detergent/friction modifier additive concentrate for gasoline that provides all of fuel economy enhancement, deposit control and friction reduction. In addition it should be stable over the temperature range at which the concentrate may feasibly be stored, and which does not adversely affect the performance and properties of the finished gasoline or engine in which the gasoline is used, and in particular, does not lead to increased IVD problems.